1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to semiconductor workpiece holder and processing chambers using the same.
2. Description of the Related Art
Tube furnaces are widely used in semiconductor processing for a variety of different types of process steps. Examples of tube furnace processes are legion and include devices suited for chemical vapor deposition (“CVD”), annealing, and oxidation to name just a few. In many conventional tube reactors, scores of semiconductor wafers are positioned in a rack or boat composed of quartz. Conventional boat designs usually consist of three or more rails connected at each end to a cap. The rails are spaced apart and provided with a plurality of laterally spaced rings or inwardly projecting tabs that are designed to support the wafers. After loading, the boat is positioned in the reactor and, depending upon the particular process involved, reactive gases are introduced therein and exhausted therefrom.
Conventional boat designs exhibit several disadvantages. In those conventional boat designs that include a plurality of vertically spaced rings for supporting individual wafers, the rings themselves are subject to frequent fracture and warping as a result of thermal stresses. A fractured ring requires the boat to be taken out of service and subjected to a time intensive and costly repair procedures. Ring warping can skew the characteristics of films deposited on the wafer. This skewing in film properties stems largely from the fact that many types of CVD processes are mass transfer limited. In such processes, the pitch or spacing between the wafers in the boat is critical in order to reduce the impact of mass transfer limitations. If one or more rings supporting the wafers become warped, the critical spacing may be changed and result in poor film quality during deposition.
In those conventional designs that incorporate inwardly projecting tabs in lieu of rings, there remains the problem of localized cooling of the wafers as a result of conductive heat transfer between the wafer and the tabs. Conventional tab designs present a relatively large footprint in contact with the wafer, resulting in conductive heat transfer that is sufficient to produce a localized cooling of the wafer. This localized cooling produces a perturbation in the boundary layer formation in the vicinity of the tab. The disruption in the boundary layer formation can again lead to unanticipated film characteristics, particularly in mass transfer limited reactions, such as high temperature and medium temperature oxidation processes.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.